The present invention relates an apparatus and a method of spraying to form a coating on flat or curved substrates, for example, either as part of the direct formation of metallic or ceramic coatings such as superconductive or piezo-electric layers or for the production of targets for sputtering magnetrons having coatings which are precursors of such layers.
From EP-A-286 135 it is known to flame spray complex ceramic materials onto a substrate such as a tape to form a superconducting layer. It is suggested to pre-heat the substrate to temperatures above 540xc2x0 C. and to cool the coating slowly. It is further recommended to treat the coating in an atmosphere containing one of the components of the superconducting ceramic. An oxy-acetylene flame is used for the flame spraying. Thickness of up to 3 mm are described.
It is also known from U.S. Pat. No. 5,196,400 to plasma spray a coating onto a target for use in a sputtering magnetron to sputter a Yxe2x80x94Baxe2x80x94CuO superconductor coating. Deposition of only a thin target coating of 0.5 mm is reported.
The production of superconducting powders using flame spraying is reported in U.S. Pat. No. 5,140,005. An oxy-acetylene flame is used. It is tacitly accepted that the high temperature of the flame changes the stoichiometric ratios of the components and that this has to be compensated by increasing the more volatile components in the original mixtures. U.S. Pat. No. 5,045,365 describes a method of cooling a oxy-acetylene flame-sprayed substrate with water. Without special precautions, water cooling is unsuitable for superconductors due to the water vapour produced.
EP-A-355 736 describes production of flat targets with metal oxides up to a layer thickness of 3 mm. WO 98/0833 describes the production of  less than 20 micron thick layers of superconducting metal oxide mixtures.
The article by Murakami et. al. xe2x80x9cRapidly Solidified Thick Deposit Layers of Fexe2x80x94Cxe2x80x94Mo Alloys by Flame Sprayingxe2x80x9d describes up to 1.5 mm thick rapidly cooled thick layers of Fexe2x80x94Cxe2x80x94Mo alloys by flame spraying. Special precautions were taken to produce dense layers, e.g. direct application of cryogenic gas on the coating during application.
EP-A-586 809 describes the metal spraying application of a layer of relatively homogeneous material (nickel coated silicon) which is much easier to handle than the heterogeneous oxide mixtures contemplated by the present invention. Layer thicknesses of up to 8 mm are described but 3 to 5 mm is preferred. Various layers are proposed including a Nixe2x80x94Al layer for improving adhesion between the deposited layer and the substrate. A Nixe2x80x94Al adhesion promoter is known from DE-A-33 18 828.
Plasma spraying of superconducting materials is described in EP-A-2887 11 up to a thickness of 250 micron.
It is an object of the present invention to provide an apparatus and a method of spraying heterogeneous metal oxides to form a ceramic coating on flat or curved substrates.
It is a further object of the present invention to provide an apparatus and a method of spraying heterogeneous metal oxides to form a thick walled ceramic coating on flat or curved substrates which is structurally sound.
It is a further object of the present invention to provide an apparatus and a method of spraying to form a thick walled coating of a superconducting ceramic material.
It is still a further object of the present invention to provide an apparatus and a method of spraying suitable for forming a thick walled ceramic coating on flat or curved targets to be used in a sputtering magnetron.
It is still another object of the present invention to provide a method of producing a (magnetron) vacuum sputtering target as well as the target itself with improved thermal and electrical conductivity and high mechanical strength using a spraying process employing dedicated powder formulations.
One aspect of the present invention is to provide a substrate with a coating of a combination of metal oxides having a thickness greater than 3 mm more preferably greater than 5 mm and most preferably greater than 8 mm. Preferably, the coating is deposited by spraying, e.g. flame or plasma spraying. Preferably, the substrate is cylindrical and is more preferably is suitable as a cylindrical target substrate for a sputtering magnetron. The combination of oxides preferably comprises at least a superconductive precursor or a superconductor. The thermal conductivity of the deposited material is preferably between 1 and 5 Wmxe2x88x921Kxe2x88x921. When deposited on a steel substrate the thermal conductivity of the composite preferably lies within the range 25 to 125 Wmxe2x88x921Kxe2x88x921. These values are particularly preferred for YBa2Cu3O7 coatings. Preferably, an adhesion promoter layer is applied onto the substrate before application of the coating of the metal oxide combination. The adhesion promoter may be a layer of Nixe2x80x94Al or a layer of an In-alloy, for example. The deposited coating is preferably impact resistant, e.g. withstands impact of a 0.036 kg steel ball from a height of 2 meters. Preferably, about 20% or up to 30% of a noble metal is included in the oxide material to improve electrical and thermal properties of the deposited layer. The noble metal is preferably silver. The noble metal may in included as a salt or oxide, e.g. silver nitrate or silver oxide, in the material to be sprayed. Preferably, the electrical resistivity of the deposited layer is lower than 15xc3x9710xe2x88x926 Ohm.m, more preferably lower than 10xc3x9710xe2x88x926 and most preferably less than 5xc3x9710xe2x88x926 Ohm.m. Values below 1xc3x9710xe2x88x926 Ohm.m can be achieved. Up to 30% of a noble metal such as silver may be added to lower the resistivity. These values are particularly preferred for YBa2Cu307 coatings.
The electrical, thermal and mechanical properties of the coating deposited in accordance with the present invention should be sufficient that the deposited layer can be applied to a suitable substrate by means of a sputtering magnetron preferably at a static sputtering deposition speed of at least 5 nm/minute, more preferably, at 20 nm/minute and most preferably at at least 40 nm/minute.
When a superconductor precursor or a superconductive material is deposited, at least 10% of the coating is in the superconducting phase, more preferably 15%. This may be assisted by a subsequent limited thermal treatment, e.g. 3 hours and 940xc2x0 C., after deposition.
The present invention also includes a method of depositing by spraying a superconductor precursor layer onto a cylindrical target for a sputtering magnetron, the layer having a thickness of at least 3 mm, and at least 10% of the layer being in a superconductive phase. The present invention also includes a method of depositing by spraying a layer onto a substrate, the layer having a thickness of at least 5 mm, and the coating comprising metal oxides.
In accordance with one aspect of the present invention a flame spraying apparatus is provided for depositing a metal oxide combination onto a substrate to produce a coating thereon, comprising: a burner for producing a flame; an inlet for feeding material to be sprayed through the flame, the flame imparting a temperature to the material to be sprayed of 1500xc2x0 C. or less, preferably 1200xc2x0 C. or less. Preferably the temperature imparted may be a little higher than the melting point of the powder to be sprayed, e.g. 600 to 1000xc2x0 C. for some metal oxides. Preferably, the thickness of the deposited coating is greater than 3 mm more preferably greater than 5 mm and most preferably greater than 8 mm.
Another aspect of the present invention is to provide a flame spraying apparatus for depositing a metal oxide combination onto a substrate to produce a coating thereon, comprising: a flame spraying gun; and a cooling system for the substrate, the cooling system including a device for bringing a cryogenic fluid into contact with the substrate. Preferably, the thickness of the deposited coating is greater than 3 mm more preferably greater than 5 mm and most preferably greater than 8 mm. The input material for the sprayer may be a liquid solution of soluble compounds (e.g. nitrates) which decompose thermally into ceramic component oxides, liquid slurries of the ceramic components or metal powders, or dry metal or ceramic powders or precursors of the ceramic components, e.g. nitrates, of such powders.
The present invention may provide a method of flame spraying a combination of metal oxide materials onto a substrate to produce a coating thereon, comprising: generating a flame; feeding the material to be sprayed through the flame, the flame imparting a temperature to the material to be sprayed of 1500xc2x0 C. or less, preferably 1200xc2x0 C. or less. Preferably the temperature imparted may be a little higher than the melting point of the powder to be sprayed, e.g. 600 to 1000xc2x0 C. for some metal oxides.
The present invention may also provide a method of flame spraying metal oxide combinations onto a substrate to produce a coating thereon, comprising: generating a flame for spraying the materials; and cooling the substrate by bringing a cryogenic fluid into contact with the substrate.
The present invention may also provide a method of flame spraying a superconducting ceramic material or a precursor thereof onto a substrate to produce a coating thereon, comprising: generating a flame for spraying the ceramic material; depositing the coating on the substrate; and during deposition of the coating, cooling the substrate so that the solidified coating thereon has a temperature between room temperature (xcx9c25xc2x0 C.) and 150xc2x0 C., preferably room temperature (xcx9c25xc2x0 C.) and 100xc2x0 C. Water or cryogenic fluid cooling are particularly preferred.
One linking concept between the above methods and apparatus is control of the total heat energy into the spraying/coating system. This can be achieved by careful control of parameters which influence the energy input such as spraying distance, spray head traverse speed, rotation speed of a cylindrical substrate, powder dwell time in the hot exit plume from the spray head, particle velocity exiting the spray head, cooling method and rate of cooling the substrate during coating deposition.
The present invention also includes a method of reconditioning a target for a sputtering magnetron by flame spraying or atmospheric plasma spraying as well as a reconditioned target as made in accordance with the method. The target material or coating is preferably a ceramic coating, in particular a superconducting or superconductor precursor coating.
The final coating is preferably a metallic or ceramic layer, in particular a superconducting or piezo-electric layer or a precursor thereof. The present invention includes a method of spray drying a liquid to form a powder suitable for flame spraying. The spray dried powder may be sintered. The present invention also includes a manufacturing method for depositing a coating on a substrate comprising the steps of: spray drying a precursor liquid to form a powder and flame spraying the powder to form a coating on a substrate. The substrate may be a target for a sputtering magnetron and the final coating may sputtered onto a final substrate in the sputtering magnetron. The ceramic powder may be sintered after the spray drying step. The flame of the flame spray gun preferably imparts a temperature to the powder to be sprayed of 1500xc2x0 C. or less, preferably 1200xc2x0 C. or less. Preferably the temperature imparted may be a little higher than the melting point of the powder to be sprayed, e.g. 600 to 1000xc2x0 C. for some metal oxides. During flame spraying the target is preferably cooled by bringing a cryogenic fluid into contact with the target. In particular the cooling device should maintain the solidified coating at a temperature between room temperature (xcx9c25xc2x0 C.) and 150xc2x0 C., more preferably between room temperature (xcx9c25xc2x0 C.) and 100xc2x0 C.
The present invention includes an apparatus for spray drying a liquid to form a powder suitable for flame spraying. The present invention may also include an apparatus for depositing a coating on a substrate comprising: a spray drier for drying a precursor liquid to a powder, and a flame sprayer for flame spraying the powder to form a coating on a substrate. The substrate may be a target for a magnetron. Additionally, a sputtering magnetron for sputtering the final coating onto the final substrate using the target may be provided. The flame of the flame spray gun preferably imparts a temperature to the powder to be sprayed of slightly above the melting point of the sprayed material. Preferably the temperature imparted is 1500xc2x0 C. or less, preferably 1200xc2x0 C. or less. Temperatures of 600 to 850xc2x0 C. may be suitable for some metal oxides. In the flame sprayer a cooling system for the target is preferably provided, the cooling system including a device for bringing a cryogenic fluid into contact with the target. In particular the cooling device should maintain the solidified coating at a temperature between room temperature (xcx9c25xc2x0 C.) and 150xc2x0 C., more preferably between room temperature (xcx9c25xc2x0 C.) and 100xc2x0 C.
The above methods may be used, for example, either as part of the direct formation of superconductive or piezo-electric layers on the substrate, e.g. a tape, or for the production of coatings on targets for use in a sputtering magnetron to sputter a superconducting layer onto a final substrate. The present invention may provide oxide sputtering targets supporting very high power dissipation thus enabling high sputter deposition rates of at least 50 nm/min.
The dependent claims describe additional individual embodiments of the present invention. The present invention will now be described with reference to the following drawings.